Chagas disease (CD) is a vector-borne Neglected Zoonotic Disease (NZD) caused by a flagellate protozoan, Trypanosoma cruzi, that affects various mammalian species across America, including humans and domestic animals. However, due to an increase in population movements and new routes of transmission, T. cruzi infection is presently considered a worldwide health concern, no longer restricted to endemic countries. Dogs play a major role in the domestic cycle by acting very efficiently as reservoirs and allowing the perpetuation of parasite transmission in endemic areas. Despite the significant progress made in recent years, still there is no vaccine against human and animal disease, there are few drugs available for the treatment of human CD, and there is no standard protocol for the treatment of canine CD. In this review, we highlight human and canine Chagas Disease in its different dimensions and interconnections. Dogs, which are considered to be the most important peridomestic reservoir and sentinel for the transmission of T. cruzi infection in a community, develop CD that is clinically similar to human CD. Therefore, an integrative approach, based on the One Health concept, bringing together the advances in genomics, immunology, and epidemiology can lead to the effective development of vaccines, new treatments, and innovative control strategies to tackle CD.

Leishmaniasis is a group of parasitic diseases whose etiological agent is the protozoa Leishmania . These diseases afflict impoverished populations in tropical and subtropical regions and affect wild and domestic animals. Canine leishmaniasis is a global disease mostly caused by L. infantum . Dogs are recognized as a good reservoir since harbor the infection long before developing the disease, facilitating parasite transmission. Furthermore, there is growing evidence that dogs may also be the reservoir of the American Leishmania spp. as L. amazonensis . The innate immune response is the first defense line against pathogens, which includes natural killer (NK) and dendritic cells (DCs). By recognizing and ultimately destroying infected cells, and by secreting immune mediators that favor inflammatory microenvironments, NK cells take the lead in the infectious process. When interacting with Leishmania parasites, DCs become activated and play a key role in driving the host immune response. While activated DCs can modulate NK cell activity, Leishmania parasites can directly activate NK cells by interacting with innate immune receptors. Once activated, NK cells can engage in a bidirectional interplay with DCs. However, the complexity of these interactions during Leishmania infection makes it challenging to fully understand the underlying processes. To further explore this, the present study investigated the dynamic interplay established between monocyte‐derived DCs (moDCs) and putative NK (pNK) cells of dogs during Leishmania infection. Findings indicate that the crosstalk between moDCs exposed to L. infantum or L. amazonensis and pNK cells enhances chemokine upregulation, potentially attracting other leukocytes to the site of infection. pNK cells activated by L. infantum infected DCs upregulate IL-10 , which can lead to a regulatory immune response while moDCs exposed to L. amazonensis induced pNK cells to overexpress IFN-γ and IL-13 , favoring a mix of pro‐ and anti‐inflammatory response. In addition, parasite‐derived extracellular vesicles (EVs) can modulate the host immune response by stimulating the upregulation of anti‐inflammatory cytokines and perforin release, which may impact infection outcomes. Thus, Leishmania and parasitic EVs can influence the bidirectional interplay between canine NK cells and DCs.

Background: Proteinuria is a common finding in dogs with leishmaniosis. Although antileishmanial therapeutic protocols are widely implemented, little information is available on which treatments are most adequate for identifying proteinuria in patients with canine leishmaniosis (CanL), especially regarding the use of immunosuppressants. The aim of this study was to explore the current paradigm regarding the antiproteinuric approach adopted by veterinary practitioners in Portugal to treat dogs with CanL. Methods: A questionnaire-based study was developed using Google Forms®. The questionnaire presented a number of different hypothetical scenarios of CanL, and the topics surveyed included the general features of the respondents and the protocols preferred by these respondents to manage proteinuria in the presented scenarios, including choice of therapeutic drugs, appropriate diet and use of immunosuppressants, in dogs with immune-mediated glomerulonephritis. The questionnaire was internally prevalidated and diffused online over a 2-month period through Portuguese veterinary social networking groups, and data were collected for descriptive analysis. Results: A total of 86 veterinary practitioners responded to the survey. When exposed to theoretical scenarios of proteinuria in dogs with CanL at stages IIb, III and IV (LeishVet guidelines), 16.3%, 62.8% and 93.8% of the respondents, respectively, answered that they would treat it. The dog was started on a renal diet as therapy by 28.6%, 83.3% and 97.4% of respondents, respectively. Angiotensin-converting enzyme inhibitors (ACEI) were prescribed by 100%, 85.2% and 78.9% of respondents as first-choice drugs for CanL at stages IIb, III and IV, respectively, with ACEI used in monotherapy by 64.3%, 40.7% and 46.1%. In comparison, protocols using ACEI in combination with other compounds were chosen by 7.1%, 33.3% and 39.5% of respondents, and combination therapy which did not include ACEI was the choice of 0.0%, 12.9% and 14.5%. Regarding immunosuppressants, 44.2% of the respondents answered they would prescribe them, with 97.4% electing for prednisolone and 5.3% choosing mycophenolate mofetil. Conclusions: Among the veterinary practitioners who responded, proteinuria treatment was considered since stage IIb CanL, although implementation of a therapeutic approach was more evident in advanced CanL stages. ACEI were the first-choice drugs, particularly for the treatment of stage IIb CanL; in advanced stages, a combination of antiproteinuric drugs was more often used. Immunosuppressant use was controversial, although when applied, prednisolone was the preferred choice. These findings reinforce the small body of evidence that supports the use of such drugs and the need to further explore their role in CanL. Graphical

Leishmaniasis caused by Leishmania infantum is a zoonotic disease endemic in many regions worldwide. The antigen-presenting dendritic cells (DCs) bridge the innate and adaptive immune response by activating T lymphocytes. Therefore, the present study examines whether T lymphocyte activation can be directed by autologous DCs primed by extracellular vesicles (EVs) derived from L. infantum. For this, lymphocytes were co-cultured with monocyte-derived DCs (moDCs) that were primed by EVs. moDC signaling and activation were examined by gene expression of toll-like receptors and cytokines. The antigen-presentation ability was analyzed through major histocompatibility complex molecules, and T cell subpopulations were explored by immunophenotyping. In co-cultures, EV-primed moDCs upregulated TLR2, TLR4, and TLR9, along with overexpression of MHC molecules. Co-cultures involving moDCs primed by EVs promoted the upregulation of both pro-inflammatory and regulatory cytokines associated with the expansion of non-conventional regulatory and central memory T cell subsets within the CD8⁺ T cell subpopulation. These findings suggest that activated moDCs can modulate cytotoxic lymphocytes, thereby promoting a balanced inflammatory microenvironment counterbalanced by a concurrent regulatory immune response. Thus, cell-based immune strategies using moDCs loaded with Leishmania-derived EVs represent a potential first step toward the development of innovative and personalized immune prophylactic and therapeutic approaches for leishmaniasis.